Tuesday June 6, 2000

Quiz 1

1. What are the three types of errors that can occur in programming?

2. What is the program javac called?

3. What does it produce?

4. What does JDK stand for?
Let us consider some basic terms related to computers.
  1. CPU - the Central Processing Unit. The CPU fetches instructions from main memory and executes them.

  2. Main Memory - the portion of memory used to hold program as they are being executed. Main memory is directly accessed by the CPU. Often main memory is a combination of RAM and ROM.

  3. ROM - Read Only Memory.

  4. RAM - Random Access Memory.

  5. Kilobyte - 1,024 (210) bytes.

  6. Megabyte - 1,048,576 (220) bytes.

  7. Megahertz - a unit of measurement for how fast a system clock is ticking. 1 megahertz is 1 million cycles per second. Some systems are rated as much as 1000 megahertz or 1 gigahertz. The original IBM PC was 4.7 MHz.

  8. microprocessor - when a CPU is manufactured on a single chip, it is referred to as a microprocessor.

  9. microcomputer - a computer based on a microprocessor.

  10. cache memory - extra fast memory that can sit between the processing unit and main memory. Instructions can be fetched faster from cache than from main memory.
Before we begin to look at specifics of the Java programming language, we need to step back for a minute and examine the basics of the binary number system. Recall that the CPU can only understand instructions that are sets of 0's and 1's. The reasons behind this go back to the design of computers. Electrical voltage can be used to encode data. Different voltages can be used to mean different things. It was found that the simplest way to use electrical voltage was to use a high and low voltage. That is, when a high electrical voltage (e.g. 5 V) is detected, the CPU can interpret that as a 1. When a low electrical voltage is detected, the CPU can interpret that as a 0.

The system of numbers that consists only of 0's and 1's is called the binary number system. We can constrast this to the ordinary decimal system, which has ten digits, 0-9. Two other important number systems are the octal number system, and the hexadecimal number system. Let us look at the particulars of these number systems.

  • The Binary System or base 2. Consists only of the digits 0 and 1. The two units are usually referred to as bits. Bits are the smallest unit that a computer can understand. Instructions at the machine level consist of sequences of 0's and 1's.

  • The Octal System or base 8. Consists of the digits 0-7.

  • The Decimal System or base 10. Consists of the digits 0-9.

  • The Hexadecimal System or base 16. This is a system of numbers with 16 digits. The ordinary digits 0-9 are used and the letters A,B,C,D,E, and F are also used. Their decimal equivalents are, respectively, 10,11,12,13,14, and 15.

    Notice that there is a special connection between three of these systems.

    Conversions between number systems.

    Consider the number 455 in base 10. The value of this number is given by

    4x102 + 5x101 + 5x100.


    In base two the number 11 has the value

    1x21 + 1x20 = 3


    in base 10.

    What we would like to consider now is how we go about converting numbers from base 2 into base 10, and vice versa.